Tutorial: Add the bias vector to the GCN model definition

[rusty1s]

Fixes #4680

[codecov]

Codecov Report

Merging #4755 (a07d44c) into master (4ea65bd) will not change coverage.
The diff coverage is n/a.

❗ Current head a07d44c differs from pull request most recent head bc482b6. Consider uploading reports for the commit bc482b6 to get more accurate results

@@           Coverage Diff           @@
##           master    #4755   +/-   ##
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  Coverage   82.47%   82.47%           
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  Files         324      324           
  Lines       17301    17301           
=======================================
  Hits        14269    14269           
  Misses       3032     3032           

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